2 * Read-Copy Update mechanism for mutual exclusion
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
18 * Copyright IBM Corporation, 2001
20 * Author: Dipankar Sarma <dipankar@in.ibm.com>
22 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
23 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
25 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
26 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
28 * For detailed explanation of Read-Copy Update mechanism see -
29 * http://lse.sourceforge.net/locking/rcupdate.html
33 #ifndef __LINUX_RCUPDATE_H
34 #define __LINUX_RCUPDATE_H
36 #include <linux/cache.h>
37 #include <linux/spinlock.h>
38 #include <linux/threads.h>
39 #include <linux/cpumask.h>
40 #include <linux/seqlock.h>
41 #include <linux/lockdep.h>
42 #include <linux/completion.h>
45 * struct rcu_head - callback structure for use with RCU
46 * @next: next update requests in a list
47 * @func: actual update function to call after the grace period.
50 struct rcu_head *next;
51 void (*func)(struct rcu_head *head);
54 /* Exported common interfaces */
55 extern void synchronize_rcu(void);
56 extern void synchronize_rcu_bh(void);
57 extern void rcu_barrier(void);
58 extern void rcu_barrier_bh(void);
59 extern void rcu_barrier_sched(void);
60 extern void synchronize_sched_expedited(void);
61 extern int sched_expedited_torture_stats(char *page);
63 /* Internal to kernel */
64 extern void rcu_init(void);
65 extern void rcu_scheduler_starting(void);
66 extern int rcu_needs_cpu(int cpu);
67 extern int rcu_scheduler_active;
69 #if defined(CONFIG_TREE_RCU)
70 #include <linux/rcutree.h>
71 #elif defined(CONFIG_PREEMPT_RCU)
72 #include <linux/rcupreempt.h>
74 #error "Unknown RCU implementation specified to kernel configuration"
75 #endif /* #else #if defined(CONFIG_CLASSIC_RCU) */
77 #define RCU_HEAD_INIT { .next = NULL, .func = NULL }
78 #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
79 #define INIT_RCU_HEAD(ptr) do { \
80 (ptr)->next = NULL; (ptr)->func = NULL; \
83 #ifdef CONFIG_DEBUG_LOCK_ALLOC
84 extern struct lockdep_map rcu_lock_map;
85 # define rcu_read_acquire() \
86 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
87 # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
89 # define rcu_read_acquire() do { } while (0)
90 # define rcu_read_release() do { } while (0)
94 * rcu_read_lock - mark the beginning of an RCU read-side critical section.
96 * When synchronize_rcu() is invoked on one CPU while other CPUs
97 * are within RCU read-side critical sections, then the
98 * synchronize_rcu() is guaranteed to block until after all the other
99 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
100 * on one CPU while other CPUs are within RCU read-side critical
101 * sections, invocation of the corresponding RCU callback is deferred
102 * until after the all the other CPUs exit their critical sections.
104 * Note, however, that RCU callbacks are permitted to run concurrently
105 * with RCU read-side critical sections. One way that this can happen
106 * is via the following sequence of events: (1) CPU 0 enters an RCU
107 * read-side critical section, (2) CPU 1 invokes call_rcu() to register
108 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
109 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
110 * callback is invoked. This is legal, because the RCU read-side critical
111 * section that was running concurrently with the call_rcu() (and which
112 * therefore might be referencing something that the corresponding RCU
113 * callback would free up) has completed before the corresponding
114 * RCU callback is invoked.
116 * RCU read-side critical sections may be nested. Any deferred actions
117 * will be deferred until the outermost RCU read-side critical section
120 * It is illegal to block while in an RCU read-side critical section.
122 static inline void rcu_read_lock(void)
130 * rcu_read_unlock - marks the end of an RCU read-side critical section.
132 * See rcu_read_lock() for more information.
136 * So where is rcu_write_lock()? It does not exist, as there is no
137 * way for writers to lock out RCU readers. This is a feature, not
138 * a bug -- this property is what provides RCU's performance benefits.
139 * Of course, writers must coordinate with each other. The normal
140 * spinlock primitives work well for this, but any other technique may be
141 * used as well. RCU does not care how the writers keep out of each
142 * others' way, as long as they do so.
144 static inline void rcu_read_unlock(void)
152 * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
154 * This is equivalent of rcu_read_lock(), but to be used when updates
155 * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
156 * consider completion of a softirq handler to be a quiescent state,
157 * a process in RCU read-side critical section must be protected by
158 * disabling softirqs. Read-side critical sections in interrupt context
159 * can use just rcu_read_lock().
162 static inline void rcu_read_lock_bh(void)
164 __rcu_read_lock_bh();
170 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
172 * See rcu_read_lock_bh() for more information.
174 static inline void rcu_read_unlock_bh(void)
178 __rcu_read_unlock_bh();
182 * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
184 * Should be used with either
185 * - synchronize_sched()
187 * - call_rcu_sched() and rcu_barrier_sched()
188 * on the write-side to insure proper synchronization.
190 static inline void rcu_read_lock_sched(void)
193 __acquire(RCU_SCHED);
196 static inline void rcu_read_lock_sched_notrace(void)
198 preempt_disable_notrace();
199 __acquire(RCU_SCHED);
204 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
206 * See rcu_read_lock_sched for more information.
208 static inline void rcu_read_unlock_sched(void)
211 __release(RCU_SCHED);
214 static inline void rcu_read_unlock_sched_notrace(void)
217 __release(RCU_SCHED);
218 preempt_enable_notrace();
223 * rcu_dereference - fetch an RCU-protected pointer in an
224 * RCU read-side critical section. This pointer may later
225 * be safely dereferenced.
227 * Inserts memory barriers on architectures that require them
228 * (currently only the Alpha), and, more importantly, documents
229 * exactly which pointers are protected by RCU.
232 #define rcu_dereference(p) ({ \
233 typeof(p) _________p1 = ACCESS_ONCE(p); \
234 smp_read_barrier_depends(); \
239 * rcu_assign_pointer - assign (publicize) a pointer to a newly
240 * initialized structure that will be dereferenced by RCU read-side
241 * critical sections. Returns the value assigned.
243 * Inserts memory barriers on architectures that require them
244 * (pretty much all of them other than x86), and also prevents
245 * the compiler from reordering the code that initializes the
246 * structure after the pointer assignment. More importantly, this
247 * call documents which pointers will be dereferenced by RCU read-side
251 #define rcu_assign_pointer(p, v) \
253 if (!__builtin_constant_p(v) || \
259 /* Infrastructure to implement the synchronize_() primitives. */
261 struct rcu_synchronize {
262 struct rcu_head head;
263 struct completion completion;
266 extern void wakeme_after_rcu(struct rcu_head *head);
269 * synchronize_sched - block until all CPUs have exited any non-preemptive
270 * kernel code sequences.
272 * This means that all preempt_disable code sequences, including NMI and
273 * hardware-interrupt handlers, in progress on entry will have completed
274 * before this primitive returns. However, this does not guarantee that
275 * softirq handlers will have completed, since in some kernels, these
276 * handlers can run in process context, and can block.
278 * This primitive provides the guarantees made by the (now removed)
279 * synchronize_kernel() API. In contrast, synchronize_rcu() only
280 * guarantees that rcu_read_lock() sections will have completed.
281 * In "classic RCU", these two guarantees happen to be one and
282 * the same, but can differ in realtime RCU implementations.
284 #define synchronize_sched() __synchronize_sched()
287 * call_rcu - Queue an RCU callback for invocation after a grace period.
288 * @head: structure to be used for queueing the RCU updates.
289 * @func: actual update function to be invoked after the grace period
291 * The update function will be invoked some time after a full grace
292 * period elapses, in other words after all currently executing RCU
293 * read-side critical sections have completed. RCU read-side critical
294 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
297 extern void call_rcu(struct rcu_head *head,
298 void (*func)(struct rcu_head *head));
301 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
302 * @head: structure to be used for queueing the RCU updates.
303 * @func: actual update function to be invoked after the grace period
305 * The update function will be invoked some time after a full grace
306 * period elapses, in other words after all currently executing RCU
307 * read-side critical sections have completed. call_rcu_bh() assumes
308 * that the read-side critical sections end on completion of a softirq
309 * handler. This means that read-side critical sections in process
310 * context must not be interrupted by softirqs. This interface is to be
311 * used when most of the read-side critical sections are in softirq context.
312 * RCU read-side critical sections are delimited by :
313 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
315 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
316 * These may be nested.
318 extern void call_rcu_bh(struct rcu_head *head,
319 void (*func)(struct rcu_head *head));
321 #endif /* __LINUX_RCUPDATE_H */